Clausenamide compounds are a species of amide compounds possessing physiological activity, which are extracted from leaves, stems, and fruits of lausena Lansium (Lour) skeels, a folk herbal medicine in South of China. The group led by Professor Huang, Liang of Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College did a lot of work on extracting active ingredients in leaves of lausena Lansium (Lour) skeels, achieved very abundant research results, and defined compounds with a structure of general formula (a) as clausenamide. To date, people have separated almost twenty species of clausenamide compounds from lausena Lansium (Lour) skeels. Then, as shown in researches for biological activities of these compounds, optically pure (−)-clausenamide has an evident effect on improving intelligence, resisting acute cerebral ischemia, and delaying tissue aging, which thereby is promising for treating senile dementia. Additionally, it was also found in the researches that the effect of optically pure (−)-clausenamide is 50 times higher than that of Piracetam, a marketed drug. However, clausenamide obtained by natural separation is a racemate, and (+)-clausenamide not only has no positive effect, but has a certain inhibiting effect. Therefore, it is important to obtain a method for inhibiting the generation of (+)-clausenamide while preparing optically pure (−)-clausenamide in large amount. After clausenamide was isolated, scientists have proposed a lot of synthetic routes, such as synthetic methods of racemic clausenamide respectively disclosed by EP0414020, CN86107090, CN90107145.5, and CN90107144.7. Furthermore, in order to obtain optically pure (−)-clausenamide, some scientists utilized chiral separation methods, such as the chiral separation method disclosed by CN 1345721A. A typical chiral separation method comprises: (1) firstly, synthesizing clausenamidone, then obtaining optically pure (−)-clausenamide by using a chiral separation method; (2) using menthol derivates as substrates of a chiral source to control Darzens reaction so as to obtain chiral intermediates; and the like.

The current methods of preparing optically pure (−)-clausenamide need to perform chiral separation or have some post-treatment problems such as chromatographic column purification, etc., which limits the industrialized production of optically pure (−)-clausenamide. Therefore, it is desired for a method of preparing optically pure (−)-clausenamide which has no need for chiral separation and has a convenient post-treatment, to achieve the industrialized requirements of optically pure (−)-clausenamide.